Catalyst structure and method of Fischer-Tropsch synthesis

ABSTRACT

The present invention includes a catalyst structure and method of making the catalyst structure for Fischer-Tropsch synthesis that both rely upon the catalyst structure having a first porous structure with a first pore surface area and a first pore size of at least about 0.1 μm, preferably from about 10 μm to about 300 μm. A porous interfacial layer with a second pore surface area and a second pore size less than the first pore size is placed upon the first pore surface area. Finally, a Fischer-Tropsch catalyst selected from the group consisting of cobalt, ruthenium, iron and combinations thereof is placed upon the second pore surface area. Further improvement is achieved by using a microchannel reactor wherein the reaction chamber walls define a microchannel with the catalyst structure placed therein through which pass reactants. The walls may separate the reaction chamber from at least one cooling chamber. The present invention also includes a method of Fischer-Tropsch synthesis.

RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 10/666,430,now U.S. Pat. No. 7,045,486, filed Sep. 19, 2003 which was a divisionalof U.S. patent application Ser. No. 10/038,228, now U.S. Pat. No.6,660,237, filed Jan. 3, 2002 which was a divisional of U.S. patentapplication Ser. No. 09/375,610, now U.S. Pat. No. 6,451,864, filed Aug.17, 1999.

FIELD OF THE INVENTION

The present invention is a catalyst structure and method of making, anda method of Fischer-Tropsch synthesis.

BACKGROUND OF THE INVENTION

Fischer-Tropsch synthesis is carbon monoxide hydrogenation that isusually performed on a product stream from another reaction includingbut not limited to steam reforming (product stream H₂/C0˜3), partialoxidation (product stream H₂/C0˜2), autothermal reforming (productstream H₂/C0˜2.5), CO₂ reforming (H₂/C0˜1) coal gassification (productstream H₂/C0˜1) and combinations thereof.

Fundamentally, Fischer-Tropsch synthesis has fast surface reactionkinetics. However, the overall reaction rate is severely limited by heatand mass transfer with conventional catalysts or catalyst structures.The limited heat transfer together with the fast surface reactionkinetics may result in hot spots in a catalyst bed. Hot spots favormethanation. In commercial processes, fixed bed reactors with smallinternal diameters or slurry type and fluidized type reactors with smallcatalyst particles (>50 μm) are used to mitigate the heat and masstransfer limitations. In addition, Fischer-Tropsch reactors are operatedat lower conversions per pass to minimize temperature excursion in thecatalyst bed. Because of the necessary operational parameters to avoidmethanation, conventional reactors are not improved even with moreactive Fischer-Tropsch synthesis catalysts. Detailed operation issummarized in Table 1 and FIG. 1.

TABLE 1 Comparison of Residence Times Effects in Fischer- TropschExperimentation Residence CH₄ Ref^((A)) Catalyst Conditions timeConversion selectivity 1 Co/ZSM-5 240° C., 20-atm, H₂/CO = 2 3.6-sec 60%21% 2 Co/MnO 220° C., 21-atm, H₂/CO = 2 0.72-sec  13% 15% 3 Co—Ru/TiO₂200° C., 20-atm, H₂/CO = 2   3-sec 61%  5% Co/TiO₂ ″   8-sec 49%  7% 4Co/TiO₂ 200° C., 20-atm, H₂/CO = 2.1   2-sec 9.5% ~9% ″  12-sec 72% ~6%5 Ru/Al₂O₃ 222° C., 21-atm, H₂/CO = 3 4.5-sec 20% ? ″ 7.2-sec 36% ″8.4-sec 45% ″ 9.6-sec 51% ″  12-sec 68% ″  14-sec 84% 6 Ru/Al₂O₃ 250°C., 22-atm, H₂/CO = 2 7.2-sec 38%  5% 7 Ru/Al₂O₃ 225° C., 21-atm, H₂/CO= 2  12-sec 66% 13% 222° C., 21-atm, H₂/CO = 3  12-sec 77% 34% Forreferences that contained results for multiple experimental conditions,the run which best matched our conversion, selectivity and/or conditionswas chosen for comparison of residence time. (A) References 1. Bessell,S., Appl. Catal. A: Gen. 96, 253 (1993). 2. Hutchings, G. J., TopicsCatal. 2, 163 (1995). 3. Iglesia, E., S. L. Soled and R. A. Fiato (ExxonRes. and Eng. Co.), U.S. Pat. No. 4,738,948, Apr. 19, 1988. 4. Iglesia,E., S. C. Reyes, R. J. Madon and S. L. Soled, Adv. Catal. 39, 221(1993). 5. Karn, F. S., J. F. Shultz and R. B. Anderson, Ind. Eng. Chem.Prod. Res. Dev. 4(4), 265 (1965). 6. King, F., E. Shutt and A. I.Thomson, Platinum Metals Rev. 29(44), 146 (1985). 7. Shultz, J. F., F.S. Karn and R. B. Anderson, Rep. Invest. - U.S. Bur. Mines 6974, 20(1967).

Literature data (Table 1 and FIG. 1) were obtained at lower H₂/CO ratio(2:1) and longer residence time (3 sec or longer). Low H₂/CO (especially2-2.5), long residence time, low temperature, and higher pressure favorFischer-Tropsch synthesis. Selectivity to CH₄ can be significantlyincreased by increasing H₂/CO ratio from 2 to 3. Increasing residencetime also has a dramatic favorable effect on the catalyst performance.Although reference 3 in Table 1 shows satisfactory results, theexperiment was conducted under the conditions where Fischer-Tropschsynthesis is favored (at least 3 sec residence time, and H₂/CO=2). Inaddition, the experiment of reference 3 was done using a powderedcatalyst on an experimental scale that would be impractical commerciallybecause of the pressure drop penalty imposed by powdered catalyst.Operating at higher temperature will enhance the conversion, however atthe much higher expense of selectivity to CH₄. It is also noteworthythat residence time in commercial Fischer-Tropsch units is at least 10sec.

Hence, there is a need for a catalyst structure and method ofFischer-Tropsch synthesis that can achieve the same or higher conversionat shorter residence time, and/or at higher H₂/CO.

SUMMARY OF THE INVENTION

The present invention includes a catalyst structure and method of makingthe catalyst structure for Fischer-Tropsch synthesis that both rely uponthe catalyst structure having a first porous structure with a first poresurface area and a first pore size of at least about 0.1 μm, preferablyfrom about 10 μm to about 300 μm. A porous interfacial layer with asecond pore surface area and a second pore size less than the first poresize is placed upon the first pore surface area. Finally, aFischer-Tropsch catalyst selected from the group consisting of cobalt,ruthenium, iron, rhenium, osmium and combinations thereof is placed uponthe second pore surface area.

Further improvement is achieved by using a microchannel reactor whereinthe reaction chamber walls define a microchannel with the catalyststructure placed therein through which pass reactants. The walls mayseparate the reaction chamber from at least one cooling chamber.

The present invention also includes a method of Fischer-Tropschsynthesis having the steps of:

-   -   (a) providing a catalyst structure having a first porous        structure with a first pore surface area and a first pore size        of at least about 0.1 μm;    -   a porous interfacial layer with a second pore surface area and a        second pore size less than the first pore size, the porous        interfacial layer placed upon the first pore surface area;    -   a Fischer-Tropsch catalyst selected from the group consisting of        cobalt, ruthenium, iron rhenium, osmium and combinations thereof        placed upon the second pore surface area; and    -   (b) passing a feed stream having a mixture of hydrogen gas and        carbon monoxide gas through the catalyst structure and heating        the catalyst structure to at least 200° C. at an operating        pressure, the feed stream having a residence time within the        catalyst structure less than 5 seconds, thereby obtaining a        product stream of at least 25% conversion of carbon monoxide,        and at most 25% selectivity toward methane.

It is an object of the present invention to provide a catalyst structurefor Fischer-Tropsch synthesis.

It is another object of the present invention to provide a method ofFischer-Tropsch synthesis having shorter residence time.

Advantages of the invention include (i) at residence time shorter thanthe prior art, higher conversions are achieved with no increase tomethane selectivity; and (ii) as residence times increase, conversionincreases and methane selectivity decreases (slightly). Surprisingly,the present invention represents an increase in conversion efficiency ofat least a factor of 3 on the basis that equivalent conversion withconventional catalyst would require correspondingly greater residencetime.

The subject matter of the present invention is particularly pointed outand distinctly claimed in the concluding portion of this specification.However, both the organization and method of operation, together withfurther advantages and objects thereof, may best be understood byreference to the following description taken in connection withaccompanying drawings wherein like reference characters refer to likeelements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of CO conversion versus residence time for prior artFischer-Tropsch processes.

FIG. 2 is a cross section of a catalyst structure according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention is a catalyst structure and method of making thecatalyst structure for Fischer-Tropsch synthesis which rely upon:

the catalyst is impregnated into a catalyst structure and calcinedthereon. In a preferred embodiment, the catalyst structure is placedwithin a reaction chamber. The reaction chamber preferably has wallsdefining at least one microchannel through which pass reactants into thereaction chamber. The walls preferably separate the reaction chamberfrom at least one cooling chamber. A microchannel has a characteristicdimension less than about 1 mm.

In order to mitigate the mass transfer limitation of the catalyststructure, the catalyst impregnation forms a porous interfacial layerthat is less than 50 μm, preferably less than 20 μm. Therefore, thediffusion path length is at least a factor of 5 shorter than forstandard catalyst particles, and the catalyst structure is more activeas indicated by the higher performance at shorter residence time. Thethinner impregnated catalyst structure also enhances heat transfer,again due to the shorter heat transfer pathway, and leads to lowerselectivity to CH₄.

In addition, because the catalyst structure is not required to beattrition resistant as would be with the catalyst particles used in afluidized bed reactor, greater porosity may be used, for exampleporosity greater than about 30%. Thus mass transfer is enhanced in thecatalyst structure.

The catalyst structure may be any geometric configuration including butnot limited to foam, felt, wad and combinations thereof. Foam is astructure with continuous walls defining pores throughout the structure.Felt is a structure of fibers with interstitial spaces therebetween. Wadis a structure of tangled strands, like steel wool.

When the first porous structure is metal, its surface is passivated andcoated with a ceramic layer using a chemical vapor deposition (CVD)method as described in U.S. patent application Ser. No. 09/123,781(E-1666A) hereby incorporated by reference. The catalyst structure ofthe present invention is depicted in FIG. 1 having a catalyst support100 of a first porous structure, a buffer layer 102 (optional), aninterfacial layer 104, and, a catalyst or catalyst layer 106. Any layermay be continuous or discontinuous as in the form of spots or dots, orin the form of a layer with gaps or holes. Continuous layer of bufferlayer 102 is preferred.

The interfacial layer 104 is a metal oxide. The metal oxide includes butis not limited to γ-Al₂O₃, SiO₂, ZrO₂, TiO₂, magnesium oxide, vanadiumoxide, chromium oxide, manganese oxide, iron oxide, nickel oxide, cobaltoxide, copper oxide, zinc oxide, molybdenum oxide, tin oxide, calciumoxide, aluminum oxide, lanthanum series oxide(s), zeolite(s) andcombinations thereof. Typically the porous support 100 has a thermalcoefficient of expansion different from that of the interfacial layer104. Accordingly, for high temperature catalysis (T>150° C.) a bufferlayer 102 may be needed to transition between the two coefficients ofthermal expansion. Another advantage of the buffer layer 102 is avoidingside reactions such as coking or cracking caused by a bare metal foamsurface. For chemical reactions which do not require large surface areasupports such as catalytic combustion, the buffer layer 102 stabilizesthe catalyst metal due to strong metal to metal-oxide interaction. Inchemical reactions which require large surface area supports, the bufferlayer 102 provides stronger bonding to the high surface area interfaciallayer 104.

The buffer layer 102 is a metal oxide that is Al₂O₃, TiO₂, SiO₂, andZrO₂ and combinations thereof. More specifically, the Al₂O₃ is α-Al₂O₃,γ-Al₂O₃ and combinations thereof. The structure of the α-Al₂O₃ ispreferred since it is most resistant to oxygen diffusion. Therefore, itis expected that resistance against high temperature oxidation can beimproved with alumina coated on the porous support 100. When the poroussupport 100 is metal foam, for example a stainless steel foam, apreferred embodiment has a buffer layer 102 formed of two sub-layers(not shown). The first sublayer (in contact with the porous support 100)is TiO₂ for good adhesion and bonding of the ceramic layers to theporous support 100. The second sublayer is α-Al₂O₃ which is used forpassivating the metal foam and is placed upon the TiO₂.

Deposition of the buffer layer 102 may be by vapor deposition includingbut not limited to chemical vapor deposition, physical vapor depositionor combinations thereof. Because the vapor deposition is conducted athigh temperatures, polycrystalline phases are formed providing goodadhesion of the metal oxide to the metal foam surface. Alternatively,the buffer layer 102 may be obtained by solution coating. For example,the solution coating has the steps of metal surface functionalizationvia hydroxide formation, followed by surface hydrolysis of alkoxides toobtain the polycrystalline phases. This solution coating may bepreferred as a lower cost method of depositing the buffer layer 102.Polycrystalline metal oxides resist flaking of layers after severalthermal cycles.

Because metal foam has web surfaces that are nonporous and smooth,deposition of the interfacial layer may be impeded. One way to mitigatethis problem is to rough the metal foam surface via chemical etching.The adhesion of high surface area gamma-alumina supported metalcatalysts to metal foam is significantly improved when metal foam isroughed via chemical etching using mineral acid solutions, for exampleHCl. Roughed web surface also shows improved resistance to the spallingof catalyst layer under thermal cyclings. The open cells of a metal foammay range from about 20 ppi (pores per inch) to about 1000 ppi and ispreferably about 80 ppi.

Catalyst metals for Fischer-Tropsch synthesis include but are notlimited to iron (Fe), cobalt (Co), ruthenium (Ru), rhenium (Re), osmium(Os) and combinations thereof.

The use of the catalyst impregnated metal foam permits residence timeless than about 5 seconds, preferably from about 1 sec to about 2 sec.The reactor will scale up with modular reactors, which will provide atleast a factor of 3 enhancement of equivalent activity.

According to the method of the present invention, residence time lessthan 5 seconds is achieved by: (a) providing a catalyst structure of ametal foam having a catalyst thereon; and (b) passing a feed streamhaving a mixture of hydrogen gas with carbon monoxide gas through thecatalyst structure and heating the catalyst structure to at least 200°C., thereby obtaining a product stream of at least 25% conversion ofcarbon monoxide, and at most 25% selectivity toward methane. In apreferred method, the catalyst structure includes a buffer layer and aninterfacial layer with the catalyst impregnated onto the interfaciallayer. The ratio of hydrogen to carbon monoxide ranges from about 1:1 toabout 6:1, preferably from about 2:1 to about 3.5:1.

Residence time less than 5 seconds may be accomplished with standardequipment but at the expense of significant energy to raise the spacevelocity of the reactants to overcome the pressure drop and poorer heattransfer leading to higher methane formation. Heat transfer from thereaction chamber is preferably enhanced by addition of microchannels onat least one reaction chamber wall on the side of the reaction chamberwall opposite the catalyst structure.

It was unexpectedly discovered that by using the catalyst structure ofthe present invention, reducing the pressure of the Fischer-Tropschreaction resulted in increased yield, less selectivity toward methane.

EXAMPLE 1

A reactor was constructed with a reaction chamber with an inlet and anoutlet. Internal reactor chamber dimensions were length 35.6 mm (1.4in), height 1.5 mm (0.060 in) and width 8 mm (0.315 in).

Catalyst impregnated metal foam was made starting with a metal foam ofstainless steel having a porosity of 90% as obtained from Astro Met,Cincinnati, Ohio. Foam metal surface was passivated and coated with aceramic layer as described above.

15 wt % Co1 wt % Ru/γ-Al₂O₃ was synthesized in house using incipientwetness method. The powdered catalyst was ball-milled overnight andslurry dip-coated on foam metal until the desired loading was achieved.The coated catalyst was dried overnight and calcined at 350° C. for fourhours.

In this experiment, two catalyst materials were used with exactly thesame composition but in different physical form. Both catalyst materialshad 15 wt % Co1 wt % Ru/γ-Al₂O₃. One was in powder form tested in amicro fixed-bed reactor according to literature specification forminimizing the heat and mass transfer resistance. The other was acatalyst impregnated metal foam tested in a single channel testing unit.

Results are shown in Table E1-1. Even though both catalysts were testedunder the identical conditions, powdered catalyst shows significantlyhigher conversion (99.6%) and higher selectivity to undesired productCH₄ (36%), apparently due to un-measured temperature excursions withincatalyst bed.

TABLE E1-1 Fischer-Tropsch Catalyst Performance Residence CH₄ CatalystConditions time Conversion selectivity Co—Ru/Al₂O₃/ 231° C., 23-atm,1-sec 17% 9.6%  foam H₂/CO = 3 Co—Ru/Al₂O₃/ 247° C., 23-atm, 1-sec 29%15% foam H₂/CO = 3 Co—Ru/Al₂O₃/ 264° C., 23-atm, 1-sec 50% 22% foamH₂/CO = 3 Co—Ru/Al₂O₃/ 264° C., 23-atm, 1-sec 49% 22% foam H₂/CO = 3Co—Ru/Al₂O₃/ 275° C., 23-atm, 1-sec 69% 24% foam H₂/CO = 3 Co—Ru/Al₂O₃/275° C., 23-atm, 2-sec 84% 9.0%  foam H₂/CO = 3 Co—Ru/Al₂O₃/ 245° C., 23atm, 1-sec 33% 12% foam H₂/CO = 3 Co—Ru/Al₂O₃/ 245° C., 23 atm, 1-sec99.6%   36% powder H₂/CO = 3

EXAMPLE 2

An experiment was conducted to demonstrate operation at variouspressures. The equipment was the same as in Example 1.

According to the literature, variation in pressure should only affecttrue residence time in Fischer-Tropsch synthesis. In other words,conventional wisdom in Fischer-Tropsch reactions is that reaction rateis proportional to pressure under identical gas hourly space velocity(GHSV).

However, as shown in Table E2-1, with the catalyst structure of thepresent invention, catalyst activity was unexpectedly enhanced as thepressure was decreased under the same temperature and pressure correctedresidence time. This surprising result is attributed to the enhancedmass and heat transfer possible with the catalyst structure of thepresent invention.

TABLE E2-1 Engineered catalyst performance for Fischer-Tropsch synthesisat 265° C. under a temperature and pressure corrected residence time of12.5 seconds. Pressure, atm Conversion, % Selectivity to CH₄, % 5 63 186 41 22 10 34 19 23 24 26

EXAMPLE 3

Use of Co or Ru alone as a catalyst on the metal foam was also testedunder the conditions of Example 1 and performance was confirmed worsethan that of bimetallic catalyst such as Co—Ru.

CLOSURE

While a preferred embodiment of the present invention has been shown anddescribed, it will be apparent to those skilled in the art that manychanges and modifications may be made without departing from theinvention in its broader aspects. The appended claims are thereforeintended to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

1. A method of conducting Fischer-Tropsch synthesis, comprising:providing a microchannel reaction chamber comprising a catalyst forFischer-Tropsch synthesis, wherein the microchannel reaction chamber hasat least one dimension of 8 mm or less; passing a feed stream comprisinga mixture of hydrogen and carbon monoxide gas through the microchannelreaction chamber with a residence time of about 1 second or less and ata temperature of 275° C. or less; wherein the mixture comprises hydrogenand carbon monoxide in a ratio of from about 2:1 to about 3.5:1; andconverting at least 50% of the carbon monoxide in the mixture tohydrocarbons.
 2. The method of claim 1 wherein the microchannel reactionchamber comprises at least one reaction chamber wall and wherein said atleast one reaction chamber wall separates the reaction chamber from atleast one cooling chamber.
 3. The method of claim 2 wherein themicrochannel reaction chamber has at least one dimension of 1 mm orless.
 4. The method of claim 3 further comprising a methane selectivityof 24% or less.
 5. The method of claim 1 wherein the catalyst comprisesCo and Ru.
 6. The method of claim 5 further comprising a methaneselectivity of 24% or less.
 7. The method of claim 6 wherein thecatalyst comprises a metal foam support.
 8. The method of claim 1wherein the catalyst comprises a metal foam support.
 9. The method ofclaim 1 wherein the temperature is in the range of 264 to 275° C. 10.The method of claim 9 further comprising a methane selectivity of 24% orless.
 11. The method of claim 1 further comprising a methane selectivityof 24% or less.
 12. The method of claim 2 wherein the temperature is inthe range of 264 to 275° C.
 13. The method of claim 2 wherein thecatalyst comprises a metal foam support.
 14. The method of claim 13wherein the microchannel reaction chamber has at least one dimension of1.5 mm or less.
 15. The method of claim 12 wherein the microchannelreaction chamber has at least one dimension of 1.5 mm or less.
 16. Themethod of claim 9 wherein the microchannel reaction chamber has at leastone dimension of 1.5 mm or less.
 17. A method of conductingFischer-Tropsch synthesis, comprising: providing a microchannel reactionchamber comprising a catalyst for Fischer-Tropsch synthesis, wherein themicrochannel reaction chamber has at least one dimension of 8 mm orless; passing a feed stream comprising a mixture of hydrogen and carbonmonoxide gas through the microchannel reaction chamber with a residencetime of about 2 seconds or less and at a temperature of 275° C. or less;wherein the mixture comprises hydrogen and carbon monoxide in a ratio offrom about 2:1 to about 3.5:1; and converting at least 50% of the carbonmonoxide in the mixture to hydrocarbons.
 18. The method of claim 17wherein the microchannel reaction chamber comprises at least onereaction chamber wall and wherein said at least one reaction chamberwall separates the reaction chamber from at least one cooling chamber.19. The method of claim 17 wherein the microchannel reaction chamber hasat least one dimension of 1 mm or less.
 20. The method of claim 18wherein the catalyst comprises Co and Ru.
 21. The method of claim 17comprising converting at least about 80% of the carbon monoxide in themixture to hydrocarbons.
 22. The method of claim 18 comprising aselectivity to methane of no more than about 10%.
 23. The method ofclaim 17 wherein the microchannel reaction chamber comprises a porousinterfacial layer having a thickness of less than 50 microns.
 24. Themethod of claim 3 wherein the microchannel reaction chamber comprises aporous interfacial layer having a thickness of less than 50 microns. 25.The method of claim 17 wherein the microchannel reaction chambercomprises a porous interfacial layer having a thickness of less than 20microns.
 26. The method of claim 3 wherein the microchannel reactionchamber comprises a porous interfacial layer having a thickness of lessthan 20 microns.
 27. The method of claim 23 wherein the porousinterfacial layer comprises a metal oxide impregnated with a catalystmetal selected from the group consisting of Fe, Co, Ru, Re, Os, andcombinations thereof.
 28. The method of claim 24 wherein the porousinterfacial layer comprises a metal oxide impregnated with a catalystmetal selected from the group consisting of Fe, Co, Ru, Re, Os, andcombinations thereof.
 29. The method of claim 25 wherein the porousinterfacial layer comprises a metal oxide impregnated with a catalystmetal selected from the group consisting of Fe, Co, Ru, Re, Os, andcombinations thereof.
 30. The method of claim 26 wherein the porousinterfacial layer comprises a metal oxide impregnated with a catalystmetal selected from the group consisting of Fe, Co, Ru, Re, Os, andcombinations thereof.
 31. The method of claim 17 wherein themicrochannel reaction chamber comprises a porous interfacial layerhaving a thickness of less than 20 microns.
 32. A method of conductingFischer-Tropsch synthesis, comprising: passing a feed stream comprisinga mixture of hydrogen and carbon monoxide gas through a reactionchamber; wherein the microchannel reaction chamber has at least onedimension of 8 mm or less; wherein the reaction chamber comprisescatalyst structure comprising a porous interfacial layer having athickness of less than 20 microns; and converting at least 50% of thecarbon monoxide in the mixture to hydrocarbons.
 33. The method of claim32 wherein the catalyst structure comprises a first porous structurehaving a first pore size of at least about 0.1 μm and wherein the porousinterfacial layer is disposed over the first porous structure andwherein the porous interfacial layer has a second pore size that is lessthan the first pore size; and further wherein the step of converting thecarbon monoxide is conducted at a temperature of at least 200° C. andwherein the selectivity to methane is at most 25%.
 34. The method ofclaim 33 wherein the porous interfacial layer comprises a metal oxideimpregnated with a catalyst metal selected from the group consisting ofFe, Co, Ru, Re, Os, and combinations thereof.
 35. The method of claim 32wherein the reaction chamber comprises at least one reaction chamberwall and wherein said at least one reaction chamber wall separates thereaction chamber from at least one cooling chamber; and wherein theresidence time of the mixture in the reaction channel is less than 5seconds.
 36. The method of claim 35 wherein the reaction chamber has atleast one dimension of 1 mm or less.
 37. The method of claim 34 whereinthe reaction chamber has at least one dimension of 8 mm or less.
 38. Themethod of claim 32 wherein the porous interfacial layer comprises ametal oxide impregnated with a catalyst metal selected from the groupconsisting of Fe, Co, Ru, Re, Os, and combinations thereof.
 39. Themethod of claim 38 wherein the reaction chamber comprises at least onereaction chamber wall and wherein said at least one reaction chamberwall separates the reaction chamber from at least one cooling chamber;and wherein the residence time of the mixture in the reaction channel isless than 5 seconds.
 40. The method of claim 35 wherein the reactionchamber has at least one dimension of 1 mm or less.
 41. The method ofclaim 40 wherein the residence time of the mixture in the reactionchannel is less than 2 seconds.